continuity and variety lectures by mark manteuffel, st. louis community college; clicker questions...

Continuity and varietyLectures by Mark Manteuffel, St. Louis Community College; Clicker Questions by Kristen Curran, University of Wisconsin-Whitewater

Chapter 6: Chromosomes and Cell Division

Learning Objectives

Understand and be able to describe the different types of cell division

Understand and be able to explain how through mitosis worn out old cells are replaced with fresh new duplicates

Learning Objectives

Understand and be able to explain how sperm and eggs are generated through meiosis

Describe the sex differences in the chromosomes

Discuss the consequences of deviations from the normal chromosome number

6.1 Immortal cells can spell trouble: cell division in sickness and health.

Telomeres

The telomere is like a protective cap at the end of the DNA.

Every time a cell divides, the telomere gets a bit shorter.

How might telomere length be affected in a cloned animal like “Dolly” the sheep?

1. Telomeres might be longer than normal.

2. Telomeres might be shorter than normal.

3. Telomeres might be of normal length.

4. No telomeres would be present.

Cancer

“Cancer cells are those which have forgotten how to

die.”—Harold Pinter

Take-home message 6.1

Cells have a protective section of DNA called the telomere.

Telomeres get shorter every time the cell divides.


When the telomere becomes too short, the cell dies.

Cells that rebuild the telomere with each division can become cancerous

6.2 Some chromosomes are circular, others are linear.


In prokaryotes, genetic information is carried in a single, circular chromosome.

This strand of DNA is attached at one site to the cell membrane.


Eukaryotes have much more DNA.

In eukaryotes, genetic information is organized into linear chromosomes.

Eukaryotic chromosomes float freely in the nucleus.

6.3 Prokaryotes divide by binary fission.


Bacteria divide by binary fission.

The circular chromosome duplicates itself and the cell splits into two identical new cells.

6.4 A time for everything: the cell cycle.

In which part of the cell cycle does the cell spend most of its time?

1. Interphase2. Mitosis3. G24. DNA synthesis


Eukaryotic somatic cells go through a cycle of phases.

Cell division occurs in the mitotic phase.

The rest of the cell cycle is called interphase.• Two gap phases for growth• Synthesis phase for replication of DNA

6.5 Cell division is preceded by replication.

Persistence and propagation

Replication

The process of DNA duplication

Complementarity

the characteristic that in the double-stranded DNA molecule the base on one strand always has the same pairing-partner (called the complementary base) on the other strand

Complementarity

Every “A” (adenine) pairs with “T” (thymine) and vice-versa.

Every “G” (guanine) pairs with “C” (cytosine) and vice-versa.

Mistakes sometimes occur when DNA duplicates itself?

Why might that be a good thing?

Mutation A variety of errors can occur during

replication.

Several DNA repair processes occur after replication.

If an error remains, however, the sequences in a replicated DNA molecule (including the genes) can be different from those in the parent molecule.

Review: If an incorrect base is placed in the DNA during replication, the mutation would be called a:

1. deletion2. insertion3. substitution4. chromosomal

breakage


Every time a cell divides, the cell’s DNA must duplicate itself so that both new cells have all the DNA of the parent cell.

This process of DNA duplication is called replication.

Errors in replication can lead to changes in the DNA sequence called mutations.

6.6 Most cells are not immortal: mitosis generates replacements.

What is dust?

Why is it your fault?

Mitosis has just one purpose:

To enable cells to generate new, genetically identical cells.

There are two different reasons for this need:

1. Growth2. Replacement

Apoptosis

the pre-planned process of cell suicide

Certain cells are targeted for apoptosis.

Mitosis

The number of (somatic) cells that must be replaced by mitosis every day is huge.

The rate at which mitosis occurs varies dramatically.

What cellular process listed below might involve mitosis?1. Wound healing2. Making insulin3. Glucose transport4. Muscle contraction


Cells use mitosis to generate new, genetically identical cells.

This makes it possible for organisms to grow and to replace cells that die.

6.7 Overview

Mitosis leads to duplicate cells.

Parent cells daughter cells


Mitosis is the process by which cells duplicate themselves.

It occurs in four steps, followed by the replication of chromosomes.

One parent cell becomes two daughter cells.

6.8 The Details

Mitosis is a four-step process.

Preparation for Mitosis: The

Chromosomes Replicate

Animal chromosomes are linear.

So why do they look like the letter “X” in pictures?

Sister Chromatids

A chromosome and its identical replicated copy, joined at the

centromere.

Classroom Catalyst

Mitosis Card Game

Which of the following processes occurs first during mitosis?1. Sister chromatids separate.2. Sister chromatids line up at

the equator of the cell.3. Chromosomes condense.4. Cytokinesis

Put the events of mitosis listed below in the correct order.

1. 12342. 32143. 32414. 3124

1. Sister chromatids separate.2. Sister chromatids line up at

the equator of the cell.3. Chromosomes condense.4. Cytokinesis

6.9 Cell division out of control means cancer.

Cancer

unrestrained cell growth and division

can lead to tumors

second leading cause of death in the United States

Tumor Growth

unregulated cell division

Cancer cells have several features that distinguish them from normal cells, including…

Benign and Malignant Tumors

What is cancer?

How does it usually cause death?

Why is the treatment for cancer often considered as bad as the disease?

Why do chemotherapy and radiation affect cancer cells and normal cells?

1. Both treatments affect cells that are in G1.

2. Both treatments affect cells that are actively dividing.

3. Both treatments affect cells that have a high metabolism.

4. Both treatments affect cells that have stopped dividing.


Cancer is unrestrained cell growth and division.

Cancer can lead to large masses of cells called malignant tumors that can cause serious health problems.

Treatment focuses on killing or slowing the division of the cells using chemotherapy and/or radiation.

6-10. Sexual reproduction requires special cells made by meiosis.

Meiosis

gametes

diploid

haploid

maintains a stable genome size in a species

Meiosis achieves more than just a reduction in the amount of genetic material in gametes.

You have two copies of every gene!

Meiosis has two important features:

1. It reduces the amount of genetic material in gametes.

2. It produces gametes that all differ from each other with respect to the combinations of alleles they carry.

A human sperm contains ___ chromosomes, but when the sperm fuses with an egg, the total number of chromosomes is ____.

1. 46; 922. 15; 303. 23; 464. 23; 23


In sexually reproducing organisms, gametes are produced through meiosis.

Gametes have half as much genetic material as the parent cell.

Gametes carry different combinations of alleles.

6.11 Sperm and egg are produced by meiosis: the details, step-by-step.

Mitosis occurs almost everywhere in an animal’s

body. Meiosis only occurs in one place.

Where?

Meiosis starts with a diploid cell.

one of the specialized diploid cells in the gonads

Meiosis starts with a diploid cell.

a homologous pair, or homologues• the maternal and paternal copies of a

chromosome

Chromosomes are duplicated.

sister chromatids• Each strand and its identical

duplicate, held together at the centromere.

Cells undergoing meiosis divide twice.

There are two major parts to meiosis:

1. The homologues are separated.

2. Each of the two new cells divides again, separating the sister chromatids into two even newer cells

Meiosis Division 1

Separating the homologues

1. Prophase I

The most complex of all of the phases of meiosis

Crossing over

2. Metaphase I

Each pair of homologous chromosomes moves to the equator of the cell.

3. Anaphase I

Beginning of the first cell division that occurs during meiosis

The homologues are pulled apart toward opposite sides of the cell.

The maternal and paternal sister chromatids are pulled to the ends of the cell in a random fashion.

3. Anaphase I

4. Telophase I and Cytokinesis

This phase is marked by the chromosomes arriving at the two poles of the cell.

The cytoplasm then divides and the cell membrane pinches the cell into two daughter cells.

4. Telophase I and Cytokinesis

Meiosis Division 2

Separating the sister chromatids

5. Prophase II

The genetic material once again coils tightly making the chromatids visible under the microscope.

It is important to note that in the brief interphase prior to prophase II, there is no replication of any of the chromosomes.

6. Metaphase II

The sister chromatids (each appearing as an X) move to the center of the cell.

7. Anaphase II

The fibers attached to the centromere begin pulling each chromatid in the sister chromatid pair toward opposite ends of each daughter cell.

8. Telophase II

The cytoplasm then divides, the cell membrane pinches the cell into two new daughter cells, and the process comes to a close.

Outcome of Meiosis

the creation of four haploid daughter cells, each with just one set of chromosomes which contains a completely unique combination of traits

Classroom Catalyst

Meiosis Card Game

What is the final outcome of meiosis?

1. Four genetically identical cells

2. Four genetically non-identical cells

3. Two genetically identical cells

4. Two genetically non-identical cells

What event or events occur during meiosis to make each resulting gamete genetically non-identical?

1. Crossing over between homologous chromosomes.

2. Alignment between pairs of homologous chromosomes can differ during Metaphase I (independent assortment).

3. Separation of sister chromatids during Anaphase II.

4. Both 1 and 2 are correct.5. All of the above.


Meiosis occurs only in gamete-producing cells.

It occurs after DNA replication and consists of two rounds of cellular division.


In the first round, homologous pairs of sister chromatids separate and in the second round, sister chromatids separate.

The final product of meiosis in a diploid organism is four haploid gametes.

6.12 Male and female gametes are produced in slightly different ways.

How do you distinguish a male from a female?


In species with two sexes, females produce the larger gamete and males produce a smaller gamete.

Male and female gametes both end up with just one copy of each chromosome.

6.13 Crossing over and meiosis are important sources of variation


Although it doesn’t create any new traits, crossing over creates gametes with unique collections of traits.

This variation is important for evolution.

6.14 What are the costs and benefits of sexual reproduction?

Sexual reproduction advantages?

Sexual reproduction leads to offspring that are all genetically different from each other and from either parent in three different ways:

1. Crossing over in the production of gametes

2. Shuffling and reassortment of homologues during meiosis

3. Combining alleles from two parents at fertilization

Bacteria reproduce asexually, while most plants and animals reproduce sexually. Which is a better method?

Sexual reproduction disadvantages?

With asexual reproduction, the advantages and disadvantages are more or less reversed.

If an organism lives in an environment that is variable, it will most likely use _________ reproduction via the process of ___________.

1. Asexual; meiosis2. Asexual; mitosis3. Sexual; meiosis4. Sexual; mitosis


There are two fundamentally different ways that cells and organisms can reproduce:

1. Mitosis and asexual reproduction via binary fission

2. Meiosis and sexual reproduction


Asexual reproduction can be fast and efficient.

But, asexual reproduction leads to genetically identical offspring.


Sexual reproduction leads to offspring that are genetically different from one another and either parent.

But, sexual reproduction takes more time and energy and can be risky.

Which parent determines the sex of their baby?

Why?

6-15. How is sex determined in humans?

Sex Chromosomes


In humans, the sex chromosomes carry information that directs a growing fetus to develop as a male or a female.•male if the Y chromosome is

present•female if there is not Y

chromosome

6.16 The sex of the offspring is determined in a variety of ways in other species.

The sex of the offspring is determined in a variety of ways in other species.

The sex ratio (number of females vs. males) of which of the following species might be most affected by global warming?

1. Humans2. Bees3. Birds4. Turtles


A variety of methods are used for sex determination in animal and plant species including:

• the presence or absence of sex chromosomes

• the number of chromosome sets

• environmental factors

6.17 Down syndrome can be detected before birth: karyotypes reveal an individual’s entire chromosome set.

karyotype • a display of an individual’s complete set

of chromosomes

1. Amniocentesis

2. Chorionic Villus Sampling (CVS)

Tissue is removed from the placenta.

Because the fetus and placenta both develop from the same fertilized egg, their cells contain the same genetic composition.

Can be done several weeks earlier in the pregnancy, usually between the 10th and 12th weeks.

Nondisjunction

the unequal distribution of chromosomes during meiosis

error of cell division that creates a gamete with zero or two copies of a chromosome rather than a single copy


A karyotype is a visual display of a complete set of chromosomes.

A karyotype is a useful diagnostic tool because it can be used to identify abnormalities in a fetus’s chromosomes early in development.

Down syndrome is caused by having an extra copy of chromosome 21.

6.18 Life is possible with too many or too few sex chromosomes.

Turner Syndrome: X_

Klinefelter Syndrome: XXY

XYY Males

XXX Females

A non-disjunction is caused by a failure of chromosomes to separate properly during meiosis. Which non-disjunction listed below will cause death of the zygote in the womb?

1. Three copies of chromosome 21 (small chromosome)

2. Two copies of the X chromosome3. Two copies of the Y chromosome4. Three copies of chromosome 1

(large chromosome).


Individuals born lacking one of the sex chromosomes or with an additional X or Y chromosome usually survive.

These individuals usually have physical and/or physiological problems.

continuity and variety lectures by mark manteuffel, st. louis community college; clicker questions...

Documents

strand slide

cell division slide

synthesis slide

cancer slide

propagation slide

cancerous slide

replication of dna slide

harold pinter slide